Rubber composition and tire

ABSTRACT

Provided is a rubber composition that realizes excellent low heat generating properties while maintaining good steering stability when applied to a tire. The rubber composition of the present disclosure contains a rubber component containing a copolymer having a conjugated diene unit and an aromatic vinyl unit, and a filler, where the copolymer is a modified copolymer having a content of the aromatic vinyl unit of less than 10 mass % and modified with a modifier containing a compound represented by the formula (1).

TECHNICAL FIELD

This disclosure relates to a rubber composition and a tire.

BACKGROUND

In recent years, the demand for fuel efficiency of automobiles isincreasing because of the movement of global carbon dioxide emissionregulations caused by the social demand for energy saving and thegrowing interest in environmental problems. To meet such demand for fuelefficiency, it has been required to reduce the rolling resistance interms of tire performance. A method of optimizing a tire structure hasbeen studied as a method for reducing the rolling resistance of a tire,but a general method for reducing rolling resistance is to use amaterial with low heat generating properties as a rubber composition.

Examples of techniques of improving the low heat generating propertiesof a rubber composition include the one described in JP4478262B (PTL 1),where a rubber composition uses a modified copolymer as a rubbercomponent, and the modified copolymer is obtained by reacting a specificimino group-containing hydrocarbyloxysilane compound.

Because the dispersibility of filler is improved in the rubbercomposition of PTL 1, a certain rolling resistance-reducing effect canbe obtained when the rubber composition is applied to a tire. However,the improvement effect of the rubber composition of PTL 1 isinsufficient to meet the recent demand for fuel efficiency, and it isdesired to further improve the low heat generating properties.

Techniques of adjusting rubber components have also been developed toimprove the low heat generating properties of a rubber composition. Forexample, JP2018131560A (PTL 2) describes a rubber composition using astyrene butadiene rubber having a reduced amount of styrene as a rubbercomponent.

However, in the case of using a styrene butadiene rubber having areduced amount of styrene, it is considered that, although the low heatgenerating properties can be improved, the performance such as steeringstability when the rubber composition is applied to a tire isdeteriorated.

Further, it is conceivable to reduce the content of filler such ascarbon black to improve the low heat generating properties of a rubbercomposition. However, as in the case of using a styrene butadiene rubberhaving a reduced amount of styrene, it is considered that theperformance such as the reinforcing properties of the rubber, the wearresistance, and the steering stability when applied to a tire isdeteriorated.

Therefore, it is required to develop a technique that can greatlyimprove the low heat generating properties without deteriorating theperformance other than the low heat generating properties such as thesteering stability when applied to a tire.

CITATION LIST

Patent Literature

PTL 1: JP4478262B

PTL 2: JP2018131560A

SUMMARY Technical Problem

It could thus be helpful to provide a rubber composition that realizesexcellent low heat generating properties while maintaining good steeringstability when applied to a tire. It is also helpful to provide a tirewith improved rolling resistance and steering stability.

Solution to Problem

As a result of studies to solve the above problems, we found that, byusing a copolymer having a conjugated diene unit and an aromatic vinylunit as a rubber component and setting the content of the aromatic vinylunit of the copolymer to a small amount of less than 10 mass %, the lowheat generating properties of a rubber composition can be improved.However, when the content of the aromatic vinyl unit of the copolymer islow, there is a problem that the performance such as steering stabilitywhen the rubber composition is applied to a tire is deteriorated, asdescribed above. Therefore, as a result of further diligent research, wefound that the dispersibility of filler can be greatly improved bymodifying the copolymer with a specific modifier having oligosiloxaneand a tertiary amino group, thereby obtaining, in addition to an effectof improving the low heat generating properties by polymer improvement,further improvement in low heat generating properties and improvement insteering stability when applied to a tire because of improveddispersibility of filler.

We thus provide the following.

The rubber composition of the present disclosure is a rubber compositioncontaining a rubber component containing a copolymer having a conjugateddiene unit and an aromatic vinyl unit, and a filler, wherein

the copolymer is a modified copolymer having a content of the aromaticvinyl unit of less than 10 mass % and modified with a modifiercontaining a compound represented by the formula (1),

where R1 to R8 are each an independent alkyl group having 1 to 20 carbonatoms; L1 and L2 are each an independent alkylene group having 1 to 20carbon atoms; and n is an integer of 2 to 4.

With the above configuration, it is possible to realize excellent lowheat generating properties while maintaining good steering stabilitywhen applied to a tire.

The rubber composition of the present disclosure preferably furthercontains a conjugated diene-based rubber different from the modifiedcopolymer. This can further improve the steering stability and wearresistance when applied to a tire.

For the rubber composition of the present disclosure, the content of thearomatic vinyl unit in the copolymer is preferably 8 mass % or less.This can provide better low heat generating properties.

For the rubber composition of the present disclosure, the modifier ispreferably any one of the formulas (1a) to (1e).

This can realize both the low heat generating properties and thesteering stability when applied to a tire at a higher level.

The copolymer is preferably a modified copolymer further modified with amodifier containing a compound represented by the formula (2),

where in the formula (2), R₁ to R₃ are each independently hydrogen; analkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30carbon atoms; an alkynyl group having 2 to 30 carbon atoms; aheteroalkyl group having 1 to 30 carbon atoms; a heteroalkenyl grouphaving 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbonatoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl grouphaving 6 to 30 carbon atoms; or a heterocyclic group having 3 to 30carbon atoms, R₄ is a single bond; an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 5 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₅ is an alkyl group having 1 to 30 carbon atoms; analkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; aheteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl grouphaving 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbonatoms; an aryl group having 6 to 30 carbon atoms; a heterocyclic grouphaving 3 to 30 carbon atoms; or a functional group represented by thefollowing chemical formula (2a) or chemical formula (2b), n is aninteger of 1 to 5, when at least one of R₅ is a functional grouprepresented by the following chemical formula (2a) or chemical formula(2b), and n is an integer of 2 to 5, a plurality of R₅s may be the sameas or different from each other,

where in the formula (2a), R₆ is an alkylene group having 1 to 20 carbonatoms substituted or unsubstituted with a substituent; a cycloalkylenegroup having 5 to 20 carbon atoms substituted or unsubstituted with asubstituent; or an arylene group having 6 to 20 carbon atoms substitutedor unsubstituted with a substituent, where the substituent is an alkylgroup having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10carbon atoms, or an aryl group having 6 to 20 carbon atoms, R₇ and R₈are each independently an alkyl group having 1 to 10 carbon atoms, acycloalkyl group having 5 to 10 carbon atoms, or an alkylene grouphaving 1 to 20 carbon atoms substituted or unsubstituted with an arylgroup having 6 to 20 carbon atoms, R₉ is hydrogen; an alkyl group having1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms, X is a N, O or Satom, when X is O or S, R9 does not exist,

where in the formula (2b), R₁₀ is an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 6 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₁₁ and R₁₂ are each independently an alkyl group having 1to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms.

This can realize both the low heat generating properties and thesteering stability when applied to a tire at a higher level.

The tire of the present disclosure uses the rubber composition of thepresent disclosure described above.

With the above configuration, the rolling resistance and the steeringstability can be improved.

Advantageous Effect

According to the present disclosure, it is possible to provide a rubbercomposition that realizes excellent low heat generating properties whilemaintaining good steering stability when applied to a tire. According tothe present disclosure, it is also possible to provide a tire withimproved rolling resistance and steering stability.

DETAILED DESCRIPTION

The following describes an embodiment of the present disclosure indetail.

<Rubber Composition>

The rubber composition of the present disclosure is a rubber compositioncontaining a rubber component and a filler.

The following describes each component of the rubber composition of thepresent disclosure.

(Rubber Component)

The rubber composition of the present disclosure contains a rubbercomponent.

The rubber component contains a copolymer having a conjugated diene unitand an aromatic vinyl unit, where the copolymer is a modified copolymermodified with a modifier containing a compound represented by theformula (1).

By using a copolymer that has been modified with a modifier containing acompound represented by the formula (1) containing oligosiloxane, whichis a filler-affinity functional group, and a tertiary amino group as therubber component, the dispersibility of the filler in the rubbercomposition such as silica can be enhanced. As a result, the low heatgenerating properties are greatly improved and the dispersibility of thefiller is improved in the rubber composition of the present disclosure,and other physical properties such as the reinforcing properties, thesteering stability when applied to a tire, and the processability canalso be improved.

In the formula (1), R1 to R8 are each an independent alkyl group having1 to 20 carbon atoms; L₁and L₂ are each an independent alkylene grouphaving 1 to 20 carbon atoms; and n is an integer of 2 to 4.

Specifically, in the formula (1), R1 to R4 may each independently be asubstituted or unsubstituted alkyl group having 1 to 20 carbon atoms.When the R1 to R4 are substituted, they may each independently besubstituted with at least one substituent selected from the groupconsisting of an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 3 to 10 carbon atoms, an alkoxy group having 1 to 10 carbonatoms, a cycloalkoxy group having 4 to 10 carbon atoms, an aryl grouphaving 6 to 12 carbon atoms, an aryloxy group having 6 to 12 carbonatoms, an alkanoyloxy group having 2 to 12 carbon atoms (alkanoyl,RaCOO⁻, where Ra is an alkyl group having 1 to 9 carbon atoms), anaralkyloxy group having 7 to 13 carbon atoms, an arylalkyl group having7 to 13 carbon atoms, and an alkylaryl group having 7 to 13 carbonatoms.

More specifically, the R1 to R4 may be a substituted or unsubstitutedalkyl group having 1 to 10 carbon atoms. More specifically, the R1 to R4may each independently be a substituted or unsubstituted alkyl grouphaving 1 to 6 carbon atoms.

In the formula (1), R5 to R8 are each independently a substituted orunsubstituted alkyl group having 1 to 20 carbon atoms. Specifically,they may each independently be a substituted or unsubstituted alkylgroup having 1 to 10 carbon atoms. More specifically, they may eachindependently be a substituted or unsubstituted alkyl group having 1 to6 carbon atoms. When substituted, they can be substituted with asubstituent as described above for R1 to R4. When R5 to R8 are not analkyl group but a hydrolyzable substituent, the bonds of N—R5R6 andN—R7R8 may be hydrolyzed to N—H in the presence of water, which mayadversely affect the processability of the polymer.

More specifically, in the compound represented by the formula (1), R1 toR4 may be a methyl group or an ethyl group, and R5 to R8 may be an alkylgroup having 1 to 10 carbon atoms.

In the present disclosure, the amino group in the compound representedby the formula (1), that is, N—R5R6 and N—R7R8 are preferably a tertiaryamino group. The tertiary amino group provides better processabilitywhen the compound represented by the formula (1) is used as a modifier.

Note that when a protecting group for protecting an amino group isbonded to the R5 to R8, or hydrogen is bonded to the R5 to R8, it may bedifficult to obtain the effect of the compound represented by theformula (1). When hydrogen is bonded, anions react with the hydrogenduring the modification and lose their reactivity, rendering themodification reaction itself impossible. When a protecting group isbonded, the modification reaction will proceed, but it is deprotected byhydrolysis during subsequent processing in a state of being bonded tothe polymer terminal, resulting in a primary or secondary amino group.The deprotected primary or secondary amino group may cause a highviscosity phenomenon in the product during subsequent composition andmay cause a decrease in processability.

In the compound represented by the formula (1), L₁ and L₂ are eachindependently a substituted or unsubstituted alkylene group having 1 to20 carbon atoms.

More specifically, L₁ and L₂ are each independently an alkylene grouphaving 1 to 10 carbon atoms. More specifically, they may be an alkylenegroup having 1 to 6 carbon atoms such as a methylene group, an ethylenegroup, or a propylene group.

For L₁ and L₂ in the compound represented by the formula (1), the effectimproves as the distance between the Si atom and the N atom in themolecule decreases. However, if Si is directly bonded to N, the bondbetween Si and N may be broken during subsequent processing, and asecondary amino group formed in this case is likely to be washed away bywater during subsequent processing. Then, it is difficult to bond amodified copolymer thus obtained to a silica filler through a member ofthe amino group that promotes the bond with a silica filler, which maydeteriorate the dispersion effect of a dispersant. Considering theimprovement effect by the length of the bond between Si and N, the L₁and L₂ are more preferably each independently an alkylene group having 1to 3 carbon atoms such as a methylene group, an ethylene group, or apropylene group, and more specifically, they may be a propylene group.Further, L₁ and L₂ may be substituted with a substituent as describedabove for R1 to R4.

The compound represented by the formula (1) is preferably, for example,any one of the compounds represented by the following formulas (1a) to(1e). This can achieve both the low heat generating properties and thesteering stability when applied to a tire at a higher level.

In the compound represented by the formula (1) of the modifier of thepresent disclosure, an alkoxysilane structure is bonded to an activatedterminal of the conjugated diene-based polymer, and a Si—O—Si structureand three or more amino groups bonded to a terminal exhibit affinity fora filler such as silica. In this way, the bond between the filler andthe modified copolymer can be promoted as compared with a conventionalmodifier containing one amino group in the molecule. Further, the degreeof bonding of the activated terminal of the conjugated diene-basedpolymer is uniform, and it is found that, when observing the change inmolecular weight distribution before and after coupling, the molecularweight distribution after coupling does not increase as compared tobefore coupling and is kept constant. Therefore, the physical propertiesof the modified copolymer itself are not deteriorated, the aggregationof the filler in the rubber composition can be prevented, and thedispersibility of the filler can be improved. As a result, theprocessability of the rubber composition can be improved. These effectscan particularly improve the fuel efficiency properties, wear propertiesand steering stability in a well-balanced manner when the rubbercomposition is applied to a tire.

Note that the compound represented by the formula (1) can be obtainedthrough a condensation reaction represented by the following reactionformula 1.

In the reaction formula 1, R1 to R8, L1 and L2, and n are the same asthose defined in the formula (1) above, and R′ and R″ are arbitrarysubstituents that do not affect the condensation reaction. For example,the R′ and R″ may each independently be the same as any one of R1 to R4.

The reaction of the reaction formula 1 is carried out under acidconditions, and the acid is not limited if it is a common one for acondensation reaction. A person skill in the art can select an optimumacid according to all kinds of process variables such as the type ofreactor in which the reaction is carried out, the starting material, andthe reaction temperature.

The copolymer modified with a modifier containing a compound representedby the formula (1) is a copolymer having a conjugated diene unit and anaromatic vinyl unit.

The conjugated diene unit and the aromatic vinyl unit can be randomlyarranged and bonded to obtain a random copolymer.

In the rubber composition of the present disclosure, it is required thatthe content of the aromatic vinyl unit of the copolymer (the massoccupied by the aromatic vinyl unit with respect to the total mass ofthe copolymer) be less than 10 mass %. This can improve the low heatgenerating properties of the rubber composition. From the sameviewpoint, the content of the aromatic vinyl unit is preferably 8 mass %or less and more preferably 7 mass % or less. From the viewpoint ofmaintaining a good level of steering stability and wear resistance whenthe rubber composition is applied to a tire, the content of the aromaticvinyl unit of the copolymer is preferably 3 mass % or more.

The type of a conjugated diene-based monomer as the conjugated dieneunit is not particularly limited. For example, it may be at least oneselected from the group consisting of 1,3-butadiene,2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadien, isoprene,and 2-phenyl-1,3-butadiene.

The type of an aromatic vinyl monomer as the aromatic vinyl unit is notparticularly limited. For example, it may be at least one selected fromthe group consisting of styrene, α-methylstyrene, 3-methylstyrene,4-methylstyrene, 4-propylstyrene, 1-vinylnaphthalene,4-cyclohexylstyrene, 4-(p-methylphenyl) styrene, and1-vinyl-5-hexylnaphthalene.

The copolymer of the modified copolymer may be a combination of theabove-mentioned conjugated diene-based monomer and aromatic vinylmonomer, among which styrene butadiene rubber is preferable. This canmore reliably realize excellent low heat generating properties withoutdeteriorating other performance and obtain excellent wet performancewhen applied to a tire.

The modified copolymer may have a narrow molecular weight distributionMw/Mn (also referred to as polydispersity index (PDI)) of 1.1 to 3.0.When the molecular weight distribution of the modified copolymer exceeds3.0 or is less than 1.1, the tensile properties and the viscoelasticitymay deteriorate when applied to the rubber composition. Considering theremarkable effect of improving the tensile properties and theviscoelasticity of the polymer by controlling the molecular weightdistribution of the modified copolymer, the molecular weightdistribution of the modified copolymer is preferably 1.3 to 2.0. Notethat the modified copolymer has a similar molecular weight distributionto that of the copolymer before being modified with the modifier.

The molecular weight distribution of the modified copolymer can becalculated from a ratio (Mw/Mn) of the weight average molecular weight(Mw) to the number average molecular weight (Mn). The number averagemolecular weight (Mn) is a common average of individual polymermolecular weights obtained by measuring the molecular weights of npolymer molecules and dividing the total of these molecular weights byn, and the weight average molecular weight (Mw) represents a molecularweight distribution of the polymer composition. The average of totalmolecular weight can be expressed in grams per mole (g/mol).

In the present disclosure, the weight average molecular weight and thenumber average molecular weight each are a polystyrene-equivalentmolecular weight analyzed by gel permeation chromatography (GPC).

The modified copolymer satisfies the above-mentioned molecular weightdistribution conditions and has a number average molecular weight (Mn)of 50,000 g/mol to 2,000,000 g/mol, where the number average molecularweight may be, more specifically, 200,000 g/mol to 800,000 g/mol. Themodified copolymer has a weight average molecular weight (Mw) of 100,000g/mol to 4,000,000 g/mol, where the weight average molecular weight maybe, more specifically, 300,000 g/mol to 1,500,000 g/mol.

When the weight average molecular weight (Mw) of the modified copolymeris less than 100,000 g/mol or the number average molecular weight (Mn)of the modified copolymer is less than 50,000 g/mol, the tensileproperties when applied to the rubber composition may deteriorate. Whenthe weight average molecular weight (Mw) exceeds 4,000,000 g/mol or thenumber average molecular weight (Mn) exceeds 2,000,000 g/mol, theworkability of the rubber composition deteriorates due to thedeterioration of the processability of the modified copolymer, which mayrender kneading difficult and may render it difficult to sufficientlyimprove the physical properties of the rubber composition.

More specifically, when the modified copolymer of one embodiment of thepresent disclosure simultaneously satisfies the conditions of weightaverage molecular weight (Mw) and number average molecular weight (Mn)as well as the molecular weight distribution, it is possible to improvethe viscoelasticity and the processability of the rubber compositionwhen applied to a composition made of rubber in a well-balanced manner.

Further, the present disclosure can provide a method of producing themodified copolymer using a modifier containing a compound represented bythe formula (1).

Specifically, the method of producing the modified copolymer may includea step 1) where an aromatic vinyl-based monomer and a conjugateddiene-based monomer are polymerized in a hydrocarbon solvent in thepresence of an organic alkali metal compound to obtain an active polymerin which an alkali metal is bonded to at least one terminal, and a step2) where the active polymer is reacted with a modifier containing acompound represented by the chemical formula 1.

The step 1) is a step for obtaining an active polymer in which an alkalimetal is bonded to at least one terminal, which can be carried out bypolymerizing an aromatic vinyl-based monomer and a conjugateddiene-based monomer in a hydrocarbon solvent in the presence of anorganic alkali metal compound.

The hydrocarbon solvent is not particularly limited, and it may be, forexample, at least one selected from the group consisting of n-pentane,n-hexane, n-heptane, isooctane, cyclohexane, toluene, benzene, andxylene.

The organic alkali metal compound may be used in an amount of 0.1 mmolto 1.0 mmol with respect to 100 g of the whole monomer.

The organic alkali metal compound is not particularly limited, and itmay be, for example, at least one selected from the group consisting ofmethyllithium, ethyllithium, propyllithium, n-butyllithium,s-butyllithium, t-butyllithium, hexyllithium, n-decyllithium,t-octyllithium, phenyllithium, 1-naphthyllithium, n-eicosyllithium,4-butylphenyllithium, 4-tolyllithium, cyclohexyllithium,3,5-di-n-heptylcyclohexyllithium, 4-cyclopentyllithium, naphthyl sodium,naphthyl potassium, lithium alkoxide, sodium alkoxide, potassiumalkoxide, lithium sulfonate, sodium sulfonate, potassium sulfonate,lithium amide, sodium amide, potassium amide, and lithiumisopropylamide.

The polymerization in the step 1) may be carried out by further adding apolar additive, if necessary, where the polar additive can be added inan amount of 0.001 parts by weight to 1.0 part by weight with respect to100 parts by weight of the whole monomer. Specifically, it can be addedin an amount of 0.005 parts by weight to 0.5 parts by weight, and morespecifically 0.01 parts by weight to 0.3 parts by weight, with respectto 100 parts by weight of the whole monomer.

The polar additive may be, for example, at least one selected from thegroup consisting of tetrahydrofuran, ditetrahydrofurylpropane, diethylether, cycloamal ether, dipropyl ether, ethylene dimethyl ether,ethylene dimethyl ether, diethyl glycol, dimethyl ether, tertiarybutoxyethoxyethane, bis (3-dimethylaminoethyl) ether,(dimethylaminoethyl) ethyl ether, trimethylamine, triethylamine,tripropylamine, and tetramethylethylenediamine.

When a conjugated diene-based monomer and an aromatic vinyl-basedmonomer are copolymerized using the polar additive in the productionmethod, the difference in reaction rates may be compensated so that theformation of random copolymer is induced to be easy.

The polymerization in the step 1) can be carried out via adiabaticpolymerization or isothermal polymerization.

As used herein, the adiabatic polymerization is a polymerization methodincluding a step of charging an organic alkali metal compound and thenperforming polymerization by self-reaction heat without arbitrarilyapplying heat, and the isothermal polymerization is a polymerizationmethod in which the organic alkali metal compound is charged and thenheat is arbitrarily applied or removed to maintain a constanttemperature of the polymer.

The polymerization may be carried out in a temperature range of 20° C.to 200° C., specifically in a temperature range of 0° C. to 150° C., andmore specifically in a temperature range of 10° C. to 120° C.

The step 2) is a modification reaction step in which the active polymeris reacted with a modifier containing a compound represented by theformula (1) to produce a modified copolymer.

At this time, the modifier containing a compound represented by theformula (1) may be the same as that described above. The compoundrepresented by the formula (1) can be used at a ratio of 0.1 mol to 2.0mol with respect to 1 mol of the organic alkali metal compound.

Further, the reaction in the step 2) is a modification reaction forintroducing a functional group into the polymer, where each reaction maybe carried out in a temperature range of 0° C. to 90° C. for 1 minute to5 hours.

The above-mentioned production method may further include one or moresteps of recovering solvent and unreacted monomers and drying after thestep 2), if necessary.

To improve the steering stability when applied to a tire, thereinforcing properties, the wear resistance and the like, the rubbercomponent preferably contains a different conjugated diene-based rubberother than the modified copolymer (hereinafter, may be referred to as“other conjugated diene-based rubber”).

The other conjugated diene-based rubber can be appropriately selectedaccording to the required performance. For example, it may be a naturalrubber (NR) containing cis-1,4-polyisoprene; a modified natural rubbersuch as epoxidized natural rubber (ENR), deproteinized natural rubber(DPNR), and hydrogenated natural rubber obtained by modifying orpurifying the above-mentioned common natural rubber; a synthetic rubbersuch as styrene-butadiene copolymer (SBR), polybutadiene (BR), andpolyisoprene (IR) ethylene-propylene copolymer rubber; or a mixture ofany one or more of the above.

The content of the modified copolymer modified with a modifiercontaining a compound represented by the formula (1) in the rubbercomponent is not particularly limited, and it may be 0.1 mass % to 100mass %, preferably 10 mass % to 100 mass %, and more preferably 20 mass% to 90 mass %. When the content of the modified copolymer is 0.1 weight% or more, the low heat generating properties can be improved whilekeeping other physical properties good. As a result, a formed productmanufactured using the rubber composition such as a tire can morereliably obtain the effects such as fuel efficiency properties, wearproperties and braking properties.

As described above, the copolymer is modified with a modifier containinga compound represented by the formula (1), but it is preferably furthermodified with a modifier containing a compound represented by theformula (2). This can further improve the dispersibility of the fillerin the rubber composition, so that both the low heat generatingproperties and the steering stability when applied to a tire can beachieved at a higher level, and the wear resistance and theprocessability can be further improved.

In the formula (2), R₁ to R₃ are each independently hydrogen; an alkylgroup having 1 to 30 carbon atoms; an alkenyl group having 2 to 30carbon atoms; an alkynyl group having 2 to 30 carbon atoms; aheteroalkyl group having 1 to 30 carbon atoms; a heteroalkenyl grouphaving 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbonatoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl grouphaving 6 to 30 carbon atoms; or a heterocyclic group having 3 to 30carbon atoms, R₄ is a single bond; an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 5 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₅ is an alkyl group having 1 to 30 carbon atoms; analkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; aheteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl grouphaving 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbonatoms; an aryl group having 6 to 30 carbon atoms; a heterocyclic grouphaving 3 to 30 carbon atoms; or a functional group represented by thefollowing chemical formula (2a) or chemical formula (2b), n is aninteger of 1 to 5, when at least one of R₅ is a functional grouprepresented by the following chemical formula (2a) or chemical formula(2b), and n is an integer of 2 to 5, a plurality of R₅s may be the sameas or different from each other.

In the formula (2a), R₆ is an alkylene group having 1 to 20 carbon atomssubstituted or unsubstituted with a substituent; a cycloalkylene grouphaving 5 to 20 carbon atoms substituted or unsubstituted with asubstituent; or an arylene group having 6 to 20 carbon atoms substitutedor unsubstituted with a substituent, where the substituent is an alkylgroup having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10carbon atoms, or an aryl group having 6 to 20 carbon atoms, R₇ and R₈are each independently an alkyl group having 1 to 10 carbon atoms, acycloalkyl group having 5 to 10 carbon atoms, or an alkylene grouphaving 1 to 20 carbon atoms substituted or unsubstituted with an arylgroup having 6 to 20 carbon atoms, R₉ is hydrogen; an alkyl group having1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms, X is a N, O or Satom, when X is O or S, R9 does not exist.

In the formula (2b), R₁₀ is an alkylene group having 1 to 20 carbonatoms substituted or unsubstituted with a substituent; a cycloalkylenegroup having 5 to 20 carbon atoms substituted or unsubstituted with asubstituent; or an arylene group having 6 to 20 carbon atoms substitutedor unsubstituted with a substituent, where the substituent is an alkylgroup having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10carbon atoms, or an aryl group having 6 to 20 carbon atoms, R₁₁ and R₁₂are each independently an alkyl group having 1 to 30 carbon atoms; analkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; aheteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl grouphaving 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbonatoms; an aryl group having 6 to 30 carbon atoms; or a heterocyclicgroup having 3 to 30 carbon atoms.

In the compound represented by the formula (2), R₁ to R₃ may be eachindependently hydrogen; an alkyl group having 1 to 10 carbon atoms; analkenyl group having 2 to 10 carbon atoms; or an alkynyl group having 2to 10 carbon atoms, R₄ may be a single bond; or an unsubstitutedalkylene group having 1 to 10 carbon atoms; R₅ may be an alkyl grouphaving 1 to 10 carbon atoms; an alkenyl group having 2 to 10 carbonatoms; an alkynyl group having 2 to 10 carbon atoms; or a functionalgroup represented by the following chemical formula (2a) or chemicalformula (2b), in the formula (2a), R₆ may be an unsubstituted alkylenegroup having 1 to 10 carbon atoms, R₇ and R₈ may be each independentlyan unsubstituted alkylene group having 1 to 10 carbon atoms, R₇ may bean alkyl group having 1 to 10 carbon atoms; a cycloalkyl group having 5to 20 carbon atoms; an aryl group having 6 to 20 carbon atoms; or aheterocyclic group having 3 to 20 carbon atoms, in the formula (2b), R₁₀may be an unsubstituted alkylene group having 1 to 10 carbon atoms, R₁₁and R₁₂ may be each independently an alkyl group having 1 to 10 carbonatoms; a cycloalkyl group having 5 to 20 carbon atoms; an aryl grouphaving 6 to 20 carbon atoms; or a heterocyclic group having 3 to 20carbon atoms.

More specifically, the compound represented by the formula (2) may be acompound represented by the following formulas (2-1) to (2-3).

When the copolymer is modified with a modifier containing a compoundrepresented by the formula (2), the modifier containing a compoundrepresented by the formula (2) is used as a modification initiator.

Specifically, by polymerizing a conjugated diene monomer and an aromaticvinyl monomer in the presence of a modifier containing a compoundrepresented by the formula (2) in a hydrocarbon solvent, a modifyinggroup derived from the compound represented by the formula (2) can beadded to the copolymer, for example.

The polymerization of the conjugated diene monomer and the aromaticvinyl monomer may be, for example, anionic polymerization.

Specifically, it may be living anionic polymerization having an anionicactive site at the polymerization terminal by a growth polymerizationreaction by anion, for example.

The polymerization may be temperature-rising polymerization, isothermalpolymerization or constant-temperature polymerization (adiabaticpolymerization). The constant-temperature polymerization is apolymerization method including a step of charging a modifier containinga compound represented by the formula (2) and then performingpolymerization by self-reaction heat without arbitrarily applying heat,the temperature-rising polymerization is a polymerization method inwhich a modification initiator is charged and then heat is arbitrarilyapplied to raise the temperature, and the isothermal polymerization is apolymerization method in which the modification initiator is charged andthen heat is applied to increase the heat or remove the heat to keep thetemperature of the polymer constant.

(Filler)

The rubber composition of the present disclosure contains a filler inaddition to the above-described rubber component.

By using a filler together with the rubber component containing themodified copolymer, the dispersibility of the filler is enhanced, theperformance such as steering stability, strength, wear resistance, andwet grip properties when the rubber composition is applied to a tire ismaintained at a high level, and excellent low heat generating propertiescan be realized at the same time.

The content of the filler is not particularly limited, but it ispreferably 10 parts by mass to 160 parts by mass and more preferably 30parts by mass to 120 parts by mass with respect to 100 parts by mass ofthe rubber component. This is because better low heat generatingproperties and wear resistance can be realized by optimizing the amountof the filler. When the content is 10 parts by mass or more, sufficientwear resistance can be obtained. When the content is 160 parts by massor less, deterioration of low heat generating properties can besuppressed.

The type of the filler is not particularly limited. For example, carbonblack, silica, and other inorganic fillers can be contained. Among theabove, the filler preferably contains at least silica. This can furtherimprove the low heat generating properties, the wear resistance, and thewet performance when used in a tire. It can also suppress deteriorationof the processability of the composition.

The CTAB (cetyltrimethylammonium bromide) specific surface area of thesilica is preferably 50 m²/g or more and preferably 350 m²/g or less.When the CTAB specific surface area of the silica is 50 m²/g or more,the wear resistance is further improved, and when the CTAB specificsurface area of the silica is 350 m²/g or less, the rolling resistanceis reduced.

The type of the silica is not particularly limited. Examples thereofinclude wet silica (hydrous silicic acid), dry silica (anhydrous silicicacid), calcium silicate, and aluminum silicate, among which wet silicais preferable. These silicas may be used alone or in combination of twoor more.

Further, examples of the silica include wet silica (hydrous silicicacid), dry silica (anhydrous silicic acid), calcium silicate, andaluminum silicate, among which wet silica is preferable. These silicasmay be used alone or in combination of two or more.

The wet silica may be precipitated silica. The precipitated silica issilica obtained by aggregating primary particles by, at an initial stageof production, advancing the reaction of a reaction solution in arelatively high temperature and neutral to alkaline pH range to growsilica primary particles and then controlling them to acidic pH range.

The content of the silica is not particularly limited, but it ispreferably 10 parts by mass to 160 parts by mass and more preferably 30parts by mass to 120 parts by mass with respect to 100 parts by mass ofthe rubber component. This is because better low heat generatingproperties and wear resistance can be realized by optimizing the amountof the filler. When the content is 10 parts by mass or more, sufficientwear resistance can be obtained. When the content is 30 parts by mass orless, deterioration of low heat generating properties can be suppressed.

The filler preferably contains carbon black in addition to the silica.This can realize better reinforcing properties and wear resistance.

Examples of the carbon black include carbon black of GPF, FEF, SRF, HAF,ISAF, IISAF, and SAF grades.

The content of the carbon black is preferably 2 parts by mass or moreand more preferably 4 parts by mass or more with respect to 100 parts bymass of the rubber component, from the viewpoint of obtaining betterwear resistance. This is because the wear resistance of the rubbercomposition can be further improved by setting the content of the carbonblack to 2 parts by mass or more with respect to 100 parts by mass ofthe rubber component. The content of the carbon black is preferably 90parts by mass or less and more preferably 70 parts by mass or less withrespect to 100 parts by mass of the rubber component. This is because,by setting the content of the carbon black to 90 parts by mass or lesswith respect to 100 parts by mass of the rubber component, it ispossible to further improve the low heat generating properties and theprocessability while maintaining the wear resistance at a high level.

Examples of the other filler include an inorganic compound representedby the following formula (A).

nM.xSiOy.zH₂O  (A)

(where M is at least one selected from metals selected from the groupconsisting of Al, Mg, Ti, Ca and Zr, oxides or hydroxides of thesemetals, hydrates of these, and carbonates of these metals; and n, x, yand z are an integer of 1 to 5, an integer of 0 to 10, an integer of 2to 5, and an integer of 0 to 10, respectively.)

Examples of the inorganic compound of the formula (A) include alumina(Al₂O₃) such as γ-alumina and α-alumina; alumina monohydrate (Al₂O₃.H₂O)such as boehmite and diaspore; aluminum hydroxide [Al(OH)₃] such asgibbsite and bayerite; aluminum carbonate [Al₂(CO₃)₃], magnesiumhydroxide [Mg(OH)₂], magnesium oxide (MgO), magnesium carbonate (MgCO₃),talc (3MgO.4SiO₂.H₂O), attapulgite (5MgO.8SiO₂.9H₂O), titanium white(TiO₂), titanium black (TiO_(2n-1)), calcium oxide (CaO), calciumhydroxide [Ca(OH)₂], aluminum oxide magnesium (MgO.Al₂O₃), clay(Al₂O₃.SiO₂), kaolin (Al₂O₃. 2SiO₂.2H₂O), pyrophyllite(Al₂O₃.4SiO₂.H₂O), bentonite (Al₂O₃.4SiO₂.2H₂O), aluminum silicate(Al₂SiO₅, Al₄.3SiO₄.5H₂O), etc.), magnesium silicate (Mg₂SiO₄, MgSiO₃,etc.), calcium silicate (Ca₂SiO₄, etc.), aluminum calcium silicate(Al₂O₃CaO.2SiO₂, etc.), calcium magnesium silicate (CaMgSiO₄), calciumcarbonate (CaCO₃), zirconium oxide (ZrO₂), zirconium hydroxide[ZrO(OH)₂.nH₂O], zirconium carbonate [Zr(CO₃)_(2]), and crystallinealuminosilicate containing hydrogen, alkali metal or alkaline earthmetal that corrects the charge like various zeolites.

(Other Components)

The rubber composition of the present disclosure may contain othercomponents in addition to the above-described rubber component andfiller if the effect of the present disclosure is not impaired.

Examples of the other component include silane coupling agent,thermoplastic resin, plasticizer, liquid rubber, age resistor,crosslinking accelerator, crosslinking agent, crosslinking promotingaid, antiozonant, and surfactant, and additives that are commonly usedin the rubber industry can be appropriately contained.

When silica is contained as the filler, the dispersibility of the silicais enhanced and better low heat generating properties and reinforcingproperties can be obtained by using the silane coupling agent togetherwith the silica.

The silane coupling agent is not particularly limited. Examples thereofinclude bis (3-triethoxysilylpropyl) tetrasulfide, bis(3-triethoxysilylpropyl) trisulfide, bis (3-triethoxysilylpropyl)disulfide, bis (2-triethoxysilylethyl) tetrasulfide, bis(3-trimethoxysilylpropyl) tetrasulfide, bis (2-trimethoxysilylethyl)tetrasulfide, 3-mercaptopropyltrimethoxysilane,3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane,2-mercaptoethyltriethoxysilane,3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide,2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide,3-trimethoxysilylpropylbenzothiazolyl tetrasulfide,3-triethoxysilylpropylbenzolyl tetrasulfide, 3-triethoxysilylpropylmethacrylate monosulfide, 3-trimethoxysilylpropyl methacrylatemonosulfide, bis (3-diethoxymethylsilylpropyl) tetrasulfide,3-mercaptopropyl dimethoxymethylsilane,dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, anddimethoxymethylsilylpropylbenzothiazolyl tetrasulfide. A mixture of anyone or more of these can also be used.

From the viewpoint of improving the reinforcing properties of the rubbercomposition, it is preferable to contain bis (3-triethoxysilylpropyl)polysulfide or 3-trimethoxysilylpropylbenzothiazyl tetrasulfide as thesilane coupling agent.

Because the rubber composition of the present disclosure uses a modifiedcopolymer where a functional group having a high affinity with asilica-based filler has been introduced into an active site as therubber component, the blending amount of the silane coupling agent canbe reduced as compared with common cases. For example, the content ofthe silane coupling agent may be 1 part by mass to 20 parts by mass withrespect to 100 parts by mass of the silica. When used in the aboverange, it is possible to sufficiently exhibit the effect as a couplingagent and prevent gelation of the rubber component at the same time.From the same viewpoint, the content of the silane coupling agent may be5 parts by mass to 15 parts by mass with respect to 100 parts by mass ofthe silica.

The rubber composition of the present disclosure may further contain athermoplastic resin. By containing the thermoplastic resin, theprocessability of the rubber composition can be improved, andadditionally, it is possible to improve the braking performance on dryroad surfaces and wet road surfaces when the rubber composition is usedfor a tire.

The type of the thermoplastic resin is not particularly limited.

Examples thereof include C5-based resin, C9-based resin, C5 to C9-basedresin, dicyclopentadiene-based resin, rosin-based resin, alkylphenol-based resin, and terpene phenol-based resin.

The C5-based resin refers to a C5-based synthetic petroleum resin andrefers to a solid polymer obtained by polymerizing a C5 fraction using aFriedel-Crafts catalyst such as AlCl₃ or BF₃. Specific examples thereofinclude a copolymer containing isoprene, cyclopentadiene,1,3-pentadiene, 1-pentene and the like as main components, a copolymerof 2-pentene and dicyclopentadiene, and a polymer mainly composed of1,3-pentadiene.

The C9-based resin refers to a C9-based synthetic petroleum resin andrefers to a solid polymer obtained by polymerizing a C9 fraction using aFriedel-Crafts catalyst such as AlCl₃ or BF₃. Specific examples thereofinclude a copolymer containing indene, methylindene, α-methylstyrene,vinyltoluene and the like as main components. The C5 to C9-based resinrefers to a C5 to C9-based synthetic petroleum resin and refers to asolid polymer obtained by polymerizing a C5 to C9 fraction using aFriedel-Crafts catalyst such as AlCl₃ or BF₃. Examples thereof include acopolymer containing styrene, vinyltoluene, α-methylstyrene, indene andthe like as main components. In the present disclosure, the C5 toC9-based resin is preferably a resin having a small amount of C9 or morecomponents from the viewpoint of the compatibility with the rubbercomponent. As used herein, the “small amount of C9 or more components”means that the C9 or more components in the total amount of the resinare less than 50 mass % and preferably 40 mass % or less.

The dicyclopentadiene-based resin is a petroleum resin usingdicyclopentadiene in the above-mentioned C5 fraction as a main rawmaterial. Examples thereof include products of “MARUKAREZ M” Series(M-890A, M-845A, M-990A, etc.) of Maruzen Petrochemical Co., Ltd.

The rosin-based resin may be a natural resin rosin such as gum rosincontained in crude turpentine and tall oil, tall oil rosin, and woodrosin, and it may be modified rosin, rosin derivative, or modified rosinderivative such as polymerized rosin, and partially hydrogenated rosinthereof; glycerin ester rosin, and partially hydrogenated rosin andfully hydrogenated rosin thereof; and pentaerythritol ester rosin, andpartially hydrogenated rosin and polymerized rosin thereof.

The alkyl phenol-based resin is a phenol-based resin having an alkylgroup. Examples thereof include an alkyl phenol-acetylene resin such asp-tert-butylphenol-acetylene resin, and an alkyl phenol-formaldehyderesin having a low degree of polymerization.

The terpene phenol-based resin is a resin that can be obtained byreacting terpenes with various phenols using a Friedel-Crafts catalyst,or by further performing condensation with formalin. The terpenes as araw material are not particularly limited, but they are preferablymonoterpene hydrocarbons such as α-pinene and limonene, more preferablythose containing α-pinene, and particularly preferably α-pinene. Aterpene phenol-based resin having a large proportion of phenolcomponents is suitable for the present disclosure. These resins may beused alone or in combination of two or more.

Further, a novolak-type phenol resin is preferably contained as thephenol resin. By containing the novolak-type phenol resin, the elasticmodulus in the rubber composition can be increased and the steeringstability can be improved without using a curing agent and withoutdeteriorating the wet performance.

The content of the thermoplastic resin is not particularly limited.However, from the viewpoint of improving the processability and thebraking properties when applied to a tire without deteriorating the wearresistance and the reinforcing properties, it is preferably 3 parts bymass to 50 parts by mass and more preferably 5 parts by mass to 30 partsby mass with respect to 100 parts by mass of the rubber component.

The age resistor may be a known one, which is not particularly limited.Examples thereof include a phenol-based age resistor, an imidazole-basedage resistor, and an amine-based age resistor. These age resistors maybe used alone or in combination of two or more.

The crosslinking accelerator may be a known one, which is notparticularly limited. Examples thereof include a thiazole-basedvulcanization accelerator such as 2-mercaptobenzothiazole,dibenzothiazyl disulfide; a sulfenamide-based vulcanization acceleratorsuch as N-cyclohexyl-2-benzothiazyl sulfenamide andN-t-butyl-2-benzothiazyl sulfenamide; a guanidine-based vulcanizationaccelerator such as diphenyl guanidine; a thiuram-based vulcanizationaccelerator such as tetramethyl thiuram disulfide, tetraethyl thiuramdisulfide, tetrabutyl thiuram disulfide, tetradodecyl thiuram disulfide,tetraoctyl thiuram disulfide, tetrabenzyl thiuram disulfide, anddipentamethylene thiuram tetrasulfide; a dithiocarbamate-basedvulcanization accelerator such as zinc dimethyldithiocarbamate; and zincdialkyldithiophosphate. These crosslinking accelerators may be usedalone or in combination of two or more.

The crosslinking agent is not particularly limited, either. Examplesthereof include sulfur and a bismaleimide compound. These crosslinkingagents may be used alone or in combination of two or more.

Examples of the types of the bismaleimide compound includeN,N′-o-phenylene bismaleimide, N,N′-m-phenylene bismaleimide,N,N′-p-phenylene bismaleimide, N,N′-(4,4′-diphenylmethane) bismaleimide,2,2-bis-[4-(4-maleimidephenoxy)phenyl]propane, andbis(3-ethyl-5-methyl-4-maleimidephenyl) methane. In the presentdisclosure, N,N′-m-phenylene bismaleimide, N,N′-(4,4′-diphenylmethane)bismaleimide and the like may be suitably used.

Examples of the crosslinking promoting aid include zinc oxide (ZnO) anda fatty acid. The fatty acid may be a saturated or unsaturated, linearor branched fatty acid. The carbon number of the fatty acid is notparticularly limited, and it may be a fatty acid with 1 to 30,preferably 15 to 30 carbon atoms, for example. Specific examples thereofinclude naphthenic acids such as cyclohexanoic acid(cyclohexanecarboxylic acid) and alkylcyclopentane with side chains;saturated fatty acids such as hexanoic acid, octanoic acid, decanoicacid (including branched carboxylic acids such as neodecanoic acid),dodecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoicacid (stearic acid); unsaturated fatty acids such as methacrylic acid,oleic acid, linoleic acid, and linolenic acid; resin acids such asrosin, tall oil acid, and abietic acid. These may be used alone or incombination of two or more. In the present disclosure, zinc oxide orstearic acid may be suitably used.

A method of producing the rubber composition of the present disclosureis not particularly limited, and the rubber composition can be obtainedby blending and kneading all the components (rubber component, filler,and other components) of the rubber composition.

<Tire>

A tire of the present disclosure uses the rubber composition of thepresent disclosure described above. By using the rubber composition ofthe present disclosure as a tire material, the obtained tire can obtaingreatly improved steering stability and rolling resistance.

In the tire of the present disclosure, the above-described rubbercomposition is specifically applied to a member, and it is particularlypreferable to apply the rubber composition to a tread among such tiremembers. A tire using the rubber composition in a tread can realize ahigh level of reinforcing properties (and thus wear resistance, steeringstability, etc.) in addition to an effect of reducing rollingresistance. Examples of a gas to be filled in the tire of the presentdisclosure include normal air, air with different oxygen partialpressure, and an inert gas such as nitrogen.

EXAMPLES

The following describes the present disclosure in more detail withreference to examples, but the present disclosure is not limited to thefollowing examples.

Example 1 and Comparative Example 1

Samples of each rubber composition are prepared according to thechemical composition listed in Table 1. The blending amount of eachcomponent is indicated in part by mass with respect to 100 parts by massof the rubber component.

The “modified SBR-1” and “modified SBR-2” in Table 1 are prepared underthe following conditions.

(Preparation of Modified SBR-1)

A cyclohexane solution of 1,3-butadiene and a cyclohexane solution ofstyrene are added to a dry, nitrogen-substituted 800 mlpressure-resistant glass container so that 67.5 g of 1,3-butadiene and7.5 g of styrene are added, and 0.6 mmol of 2,2-ditetrahydrofurylpropaneand 0.8 mmol of n-butyllithium are added to the glass container, andthen polymerization is carried out at 50° C. for 1.5 hours. At thistime, 0.72 mmol of [N,N-bis(trimethylsilyl)-(3-amino-1-propyl)](methyl)(diethoxy) silane is added to the polymerization reaction system inwhich the polymerization conversion rate has almost reached 100%, and amodification reaction is carried out at 50° C. for 30 minutes. Next, 2ml of an isopropanol 5 mass % solution of 2,6-di-t-butyl-p-cresol (BHT)is added to terminate the reaction, and the mixture is dried accordingto a conventional method to obtain modified SBR-1.

As a result of measuring the microstructure of the obtained modifiedSBR-1, the bound styrene content is 10 mass %, the vinyl content of thebutadiene portion is 40%, and the polystyrene-equivalent peak molecularweight obtained by gel permeation chromatography is 200,000.

(Production Example of Modifier)

Two vacuum-dried 4L stainless steel pressure vessels are prepared. Tothe first pressure vessel, 944 g of cyclohexane, 161 g of a compoundrepresented by the following chemical formula 2-1, and 86 g oftetramethylethylenediamine are charged to prepare a first reactionsolution. At the same time, 318 g of liquid 20 weight % n-butyllithium,and 874 g of cyclohexane are charged into the second pressure vessel toprepare a second reaction solution. At this time, the molar ratio of thecompound represented by the following chemical formula (2-1),n-butyllithium and tetramethylethylenediamine is 1:1:1. With thepressure of each pressure vessel maintained at 7 bar, the first reactionsolution is injected into a first continuous channel at an injectingrate of 1.0 g/min and the second reaction solution is injected into asecond continuous channel at an injecting rate of 1.0 g/min,respectively, in a continuous reactor using a mass flow meter. At thistime, the temperature of the continuous reactor is maintained at −10°C., the internal pressure is maintained at 3 bar using a back pressureregulator, and the residence time in the reactor is adjusted to bewithin 10 minutes. The reaction is terminated to obtain a modificationinitiator.

(Preparation of Modified SBR-2)

Continuous reactors in which three reactors are connected in series areprepared, where in the first reactor, a styrene solution in whichstyrene is dissolved in n-hexane at 60 weight % is injected at a rate of0.84 kg/h, a 1,3-butadiene solution in which 1,3-butadiene is dissolvedin n-hexane at 60 weight % is injected at a rate of 15.10 kg/h, n-hexaneis injected at a rate of 47.66 kg/h, a 1,2-butadiene solution in which1,2-butadiene is dissolved in n-hexane at 2.0 weight % is injected at arate of 10 g/h, a solution in which 2,2-(di-2(tetrahydrofuryl) propaneis dissolved in n-hexane at 10 weight % is injected as a polar additiveat a rate of 10.0 g/h, and the modification initiator produced in theabove production example is injected at a rate of 292.50 g/h. At thistime, the temperature of the first reactor is maintained at 50° C. Whenthe polymerization conversion rate reaches 43%, the polymer istransferred from the first reactor to the second reactor through atransfer pipe.

Subsequently, a 1,3-butadiene solution in which 1,3-butadiene isdissolved in n-hexane at 60 weight % is injected into the second reactorat a rate of 0.68 kg/h. At this time, the temperature of the secondreactor is maintained at 65° C. When the polymerization conversion rateis 95% or more, the polymer is transferred from the second reactor tothe third reactor through a transfer pipe.

The polymer is transferred from the second reactor to the third reactor,and a solution in which the following formula (1a) is dissolved as amodifier is charged into the third reactor (modifier: act. Li=1:1 mol).The temperature of the third reactor is maintained at 65° C.

Next, an IR1520 (BASF) solution dissolved at 30 weight % as anantioxidant is injected into the polymerization solution discharged fromthe third reactor at a rate of 170 g/h and stirred. As a result, theobtained polymer is put into warm water heated by steam and stirred, andthe solvent is removed to obtain modified SBR-2.

As a result of measuring the microstructure of the obtained modifiedSBR-2, the styrene content is 5 mass %, and the vinyl content of thebutadiene portion is 37%.

<Evaluation>

The following evaluations are performed on the obtained rubbercomposition samples of Example 1 and Comparative Example 1. The resultsare listed in Table 1.

(1) Low Heat Generating Properties

The loss tangent (tan δ) of each sample is measured under conditions ofa temperature of 30° C., a strain of 5%, and a frequency of 15 Hz usinga dynamic viscoelasticity measuring device for high frequencymanufactured by Metravib. The obtained value of tan δ is indicated as anindex with the value of Comparative Example 1 being 100 and is listed inTable 1. The smaller the index value of tan δ is, the better the lowheat generating properties are.

(2) Steering Stability

The storage shear modulus G′(Pa) of each sample is measured underconditions of 30° C., a strain of 10%, and a frequency of 15 Hz using adynamic viscoelasticity measuring device for high frequency manufacturedby Metravib. The obtained value of G′ is indicated as an index with thevalue of Comparative Example 1 being 100 and is listed in Table 1. Thelarger the index value of G′ is, the better the steering stability whenapplied to a tire is.

TABLE 1 Comparative Example 1 Example 1 Chemical NR *1 50 50 compositionModified SBR-1 50 — Modified SBR-2 — 50 Carbon black *2 7 7 Silica *3 6666 Resin *4 10 10 Processing aid A *16 2 2 Processing aid B *17 1 1Stearic acid *5 1 1 Zinc oxide *6 3 3 Oil *7 3 3 Wax *8 2 2 Age resistorA *9 2 2 Silane coupling agent *10 7 7 Age resisto B *11 2 2Vulcanization accelerator A *12 1 1 Vulcanization accelerator B *13 1 1Vulcanization accelerator C *14 2 2 Sulfur *15 2 2 Evaluation Low heatgenerating properties 100 70 Steering stability 100 107 *1: Naturalrubber, RSS #3 *2: “#80” manufactured by Asahi Carbon Co., Ltd. *3:“Nipsil HQ-N” manufactured by Tosoh Silica Corporation *4: “T-REZ RD104”manufactured by Tonen Chemical Corporation. *5: Kiriin stearic acidmanufactured by NOF CORPORATION *6: “Zinc oxide 2 types” manufactured byHAKUSUI TECH CO., LTD. *7: “Diana Process NH-70S” manufactured byIdemitsu Kosan Co., Ltd. *8: “SUNTIGHT A” manufactured by Seiko-ChemicalCo., Ltd. *9: “Antigen 6C” manufactured by Sumitomo Chemical Co., Ltd.*10: “ABC-856” manufactured by Shin-Etsu Chemical Co., Ltd.,bis-triethoxysilylpropyl-polysulfide *11: “NONFLEX RD-S” manufactured bySeiko-Chemical Co., Ltd. *12: “SOXINOL D-G” manufactured by SumitomoChemical Co., Ltd. *13: “SANCELER DM-TG” manufactured by SANSHINCHEMICAL INDUSTRY CO., LTD. *14: “NOCCELER NS-P” manufactured by OuchiShinko Chemical Industrial Co., Ltd. *15: “HK200-5” manufactured byHosoi Chemical Industry Co., Ltd. *16: “Aktiplast ® (Aktiplast is aregistered trademark in Japan, other countries, or both) PP”manufactured by LANXESS *17: “VP1405” manufactured by HAMBURG STRUCTOL

From the results in Table 1, it is understood that the sample of Example1 containing a modified copolymer modified with a modifier containing acompound represented by the formula (1) and having a low vinyl unitcontent of the modified copolymer is highly evaluated in both low heatgenerating properties and steering stability as compared with the sampleof Comparative Example 1.

INDUSTRIAL APPLICABILITY

According to the present disclosure, it is possible to provide a rubbercomposition that realizes excellent low heat generating properties whilemaintaining good steering stability when applied to a tire. According tothe present disclosure, it is also possible to provide a tire withimproved rolling resistance and steering stability.

1. A rubber composition, comprising a rubber component containing acopolymer having a conjugated diene unit and an aromatic vinyl unit, anda filler, wherein the copolymer is a modified copolymer having a contentof the aromatic vinyl unit of less than 10 mass % and modified with amodifier containing a compound represented by the formula (1),

where R1 to R8 are each an independent alkyl group having 1 to 20 carbonatoms; L1 and L2 are each an independent alkylene group having 1 to 20carbon atoms; and n is an integer of 2 to
 4. 2. The rubber compositionaccording to claim 1, wherein the rubber component further contains aconjugated diene-based rubber different from the modified copolymer. 3.The rubber composition according to claim 1, wherein a content of thearomatic vinyl unit in the copolymer is 8 mass % or less.
 4. The rubbercomposition according to claim 1, wherein the modifier is any one of theformulas (1a) to (1e).


5. The rubber composition according to claim 1, wherein the copolymer isa modified copolymer further modified with a modifier containing acompound represented by the formula (2),

where in the formula (2), R₁ to R₃ are each independently hydrogen; analkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30carbon atoms; an alkynyl group having 2 to 30 carbon atoms; aheteroalkyl group having 1 to 30 carbon atoms; a heteroalkenyl grouphaving 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbonatoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl grouphaving 6 to 30 carbon atoms; or a heterocyclic group having 3 to 30carbon atoms, R₄ is a single bond; an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 5 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₅ is an alkyl group having 1 to 30 carbon atoms; analkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; aheteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl grouphaving 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbonatoms; an aryl group having 6 to 30 carbon atoms; a heterocyclic grouphaving 3 to 30 carbon atoms; or a functional group represented by thefollowing chemical formula (2a) or chemical formula (2b), n is aninteger of 1 to 5, when at least one of R₅ is a functional grouprepresented by the following chemical formula (2a) or chemical formula(2b), and n is an integer of 2 to 5, a plurality of R₅s may be the sameas or different from each other,

where in the formula (2a), R₆ is an alkylene group having 1 to 20 carbonatoms substituted or unsubstituted with a substituent; a cycloalkylenegroup having 5 to 20 carbon atoms substituted or unsubstituted with asubstituent; or an arylene group having 6 to 20 carbon atoms substitutedor unsubstituted with a substituent, where the substituent is an alkylgroup having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10carbon atoms, or an aryl group having 6 to 20 carbon atoms, R₇ and R₈are each independently an alkyl group having 1 to 10 carbon atoms, acycloalkyl group having 5 to 10 carbon atoms, or an alkylene grouphaving 1 to 20 carbon atoms substituted or unsubstituted with an arylgroup having 6 to 20 carbon atoms, R₉ is hydrogen; an alkyl group having1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms, X is a N, O or Satom, when X is O or S, R9 does not exist,

where in the formula (2b), R₁₀ is an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 6 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₁₁ and R₁₂ are each independently an alkyl group having 1to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms.
 6. A tire, usingthe rubber composition according to claim
 1. 7. The rubber compositionaccording to claim 2, wherein a content of the aromatic vinyl unit inthe copolymer is 8 mass % or less.
 8. The rubber composition accordingto claim 2, wherein the modifier is any one of the formulas (1a) to(1e).


9. The rubber composition according to claim 2, wherein the copolymer isa modified copolymer further modified with a modifier containing acompound represented by the formula (2),

where in the formula (2), R₁ to R₃ are each independently hydrogen; analkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30carbon atoms; an alkynyl group having 2 to 30 carbon atoms; aheteroalkyl group having 1 to 30 carbon atoms; a heteroalkenyl grouphaving 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbonatoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl grouphaving 6 to 30 carbon atoms; or a heterocyclic group having 3 to 30carbon atoms, R₄ is a single bond; an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 5 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₅ is an alkyl group having 1 to 30 carbon atoms; analkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; aheteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl grouphaving 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbonatoms; an aryl group having 6 to 30 carbon atoms; a heterocyclic grouphaving 3 to 30 carbon atoms; or a functional group represented by thefollowing chemical formula (2a) or chemical formula (2b), n is aninteger of 1 to 5, when at least one of R₅ is a functional grouprepresented by the following chemical formula (2a) or chemical formula(2b), and n is an integer of 2 to 5, a plurality of R₅s may be the sameas or different from each other,

where in the formula (2a), R₆ is an alkylene group having 1 to 20 carbonatoms substituted or unsubstituted with a substituent; a cycloalkylenegroup having 5 to 20 carbon atoms substituted or unsubstituted with asubstituent; or an arylene group having 6 to 20 carbon atoms substitutedor unsubstituted with a substituent, where the substituent is an alkylgroup having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10carbon atoms, or an aryl group having 6 to 20 carbon atoms, R₇ and R₈are each independently an alkyl group having 1 to 10 carbon atoms, acycloalkyl group having 5 to 10 carbon atoms, or an alkylene grouphaving 1 to 20 carbon atoms substituted or unsubstituted with an arylgroup having 6 to 20 carbon atoms, R₉ is hydrogen; an alkyl group having1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms, X is a N, O or Satom, when X is O or S, R9 does not exist,

where in the formula (2b), R₁₀ is an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 6 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₁₁ and R₁₂ are each independently an alkyl group having 1to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms.
 10. The rubbercomposition according to claim 3, wherein the modifier is any one of theformulas (1a) to (1e).


11. The rubber composition according to claim 3, wherein the copolymeris a modified copolymer further modified with a modifier containing acompound represented by the formula (2),

where in the formula (2), R₁ to R₃ are each independently hydrogen; analkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30carbon atoms; an alkynyl group having 2 to 30 carbon atoms; aheteroalkyl group having 1 to 30 carbon atoms; a heteroalkenyl grouphaving 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbonatoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl grouphaving 6 to 30 carbon atoms; or a heterocyclic group having 3 to 30carbon atoms, R₄ is a single bond; an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 5 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₅ is an alkyl group having 1 to 30 carbon atoms; analkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; aheteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl grouphaving 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbonatoms; an aryl group having 6 to 30 carbon atoms; a heterocyclic grouphaving 3 to 30 carbon atoms; or a functional group represented by thefollowing chemical formula (2a) or chemical formula (2b), n is aninteger of 1 to 5, when at least one of R₅ is a functional grouprepresented by the following chemical formula (2a) or chemical formula(2b), and n is an integer of 2 to 5, a plurality of R₅s may be the sameas or different from each other,

where in the formula (2a), R₆ is an alkylene group having 1 to 20 carbonatoms substituted or unsubstituted with a substituent; a cycloalkylenegroup having 5 to 20 carbon atoms substituted or unsubstituted with asubstituent; or an arylene group having 6 to 20 carbon atoms substitutedor unsubstituted with a substituent, where the substituent is an alkylgroup having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10carbon atoms, or an aryl group having 6 to 20 carbon atoms, R₇ and R₈are each independently an alkyl group having 1 to 10 carbon atoms, acycloalkyl group having 5 to 10 carbon atoms, or an alkylene grouphaving 1 to 20 carbon atoms substituted or unsubstituted with an arylgroup having 6 to 20 carbon atoms, R₉ is hydrogen; an alkyl group having1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms, X is a N, O or Satom, when X is O or S, R9 does not exist,

where in the formula (2b), R₁₀ is an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 6 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₁₁ and R₁₂ are each independently an alkyl group having 1to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms.
 12. The rubbercomposition according to claim 4, wherein the copolymer is a modifiedcopolymer further modified with a modifier containing a compoundrepresented by the formula (2),

where in the formula (2), R₁ to R₃ are each independently hydrogen; analkyl group having 1 to 30 carbon atoms; an alkenyl group having 2 to 30carbon atoms; an alkynyl group having 2 to 30 carbon atoms; aheteroalkyl group having 1 to 30 carbon atoms; a heteroalkenyl grouphaving 2 to 30 carbon atoms; a heteroalkynyl group having 2 to 30 carbonatoms; a cycloalkyl group having 5 to 30 carbon atoms; an aryl grouphaving 6 to 30 carbon atoms; or a heterocyclic group having 3 to 30carbon atoms, R₄ is a single bond; an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 5 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₅ is an alkyl group having 1 to 30 carbon atoms; analkenyl group having 2 to 30 carbon atoms; an alkynyl group having 2 to30 carbon atoms; a heteroalkyl group having 1 to 30 carbon atoms; aheteroalkenyl group having 2 to 30 carbon atoms; a heteroalkynyl grouphaving 2 to 30 carbon atoms; a cycloalkyl group having 5 to 30 carbonatoms; an aryl group having 6 to 30 carbon atoms; a heterocyclic grouphaving 3 to 30 carbon atoms; or a functional group represented by thefollowing chemical formula (2a) or chemical formula (2b), n is aninteger of 1 to 5, when at least one of R₅ is a functional grouprepresented by the following chemical formula (2a) or chemical formula(2b), and n is an integer of 2 to 5, a plurality of R₅s may be the sameas or different from each other,

where in the formula (2a), R₆ is an alkylene group having 1 to 20 carbonatoms substituted or unsubstituted with a substituent; a cycloalkylenegroup having 5 to 20 carbon atoms substituted or unsubstituted with asubstituent; or an arylene group having 6 to 20 carbon atoms substitutedor unsubstituted with a substituent, where the substituent is an alkylgroup having 1 to 10 carbon atoms, a cycloalkyl group having 5 to 10carbon atoms, or an aryl group having 6 to 20 carbon atoms, R₇ and R₈are each independently an alkyl group having 1 to 10 carbon atoms, acycloalkyl group having 5 to 10 carbon atoms, or an alkylene grouphaving 1 to 20 carbon atoms substituted or unsubstituted with an arylgroup having 6 to 20 carbon atoms, R₉ is hydrogen; an alkyl group having1 to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms, X is a N, O or Satom, when X is O or S, R9 does not exist,

where in the formula (2b), R₁₀ is an alkylene group having 1 to 20carbon atoms substituted or unsubstituted with a substituent; acycloalkylene group having 5 to 20 carbon atoms substituted orunsubstituted with a substituent; or an arylene group having 6 to 20carbon atoms substituted or unsubstituted with a substituent, where thesubstituent is an alkyl group having 1 to 10 carbon atoms, a cycloalkylgroup having 5 to 10 carbon atoms, or an aryl group having 6 to 20carbon atoms, R₁₁ and R₁₂ are each independently an alkyl group having 1to 30 carbon atoms; an alkenyl group having 2 to 30 carbon atoms; analkynyl group having 2 to 30 carbon atoms; a heteroalkyl group having 1to 30 carbon atoms; a heteroalkenyl group having 2 to 30 carbon atoms; aheteroalkynyl group having 2 to 30 carbon atoms; a cycloalkyl grouphaving 5 to 30 carbon atoms; an aryl group having 6 to 30 carbon atoms;or a heterocyclic group having 3 to 30 carbon atoms.